1.) Field of the Invention
The present invention relates to a system for aerodynamic flows and, more particularly, to a system capable of controlling boundary layer flow over an aircraft wing.
2.) Description of Related Art
One of the design objectives of the aircraft designer is to ensure high aerodynamic performance over a range of flight conditions. The performance during take-off and landing is a principal design objective of transport aircraft where high-lift capability is a key requirement. Take-off and landing are especially challenging since the flows are dominated by viscous effects, which are the major determinant of aerodynamic performance, and the ability to alter the characteristics of the viscous flow is vital to the development of efficient high lift systems.
Techniques for altering the viscous flow structures are highly desirable due to the great potential for improved efficiency. A variety of fluidic actuators for manipulating viscous flows have been developed for a wide range of applications. These actuators provide oscillatory ejection and ingestion of fluid at various points on the wing surface. The great appeal of these devices is that they employ Zero-Net-Mass-Flow pulsation (“ZNMF”), i.e., no fluidic source is needed. The advantage of ZNMF is twofold: a high pressure container or bleed air from the engines (bleed reduces propulsion efficiency) is avoided, and a flow control system may be integrated without the need for complex plumbing.
Flow control systems that use oscillatory forcing may employ electrically driven fluidics or combustion powered devices. An electrical actuator uses a moving diaphragm or a piston to generate blowing/suction through an orifice, while a combustion actuator emits pulsed jets through an outlet. Generally, there are several types of electrical actuators: electromagnetic (or voice coil, like those used in speakers), electromechanical (piston driven), and piezo-electric (whereby a metallized diaphragm flexes when subjected to an electrical pulse).
For example, U.S. Pat. No. 5,988,522 to Glezer et al. discloses synthetic jet actuators for modifying the direction of fluid flow. The actuator includes a housing having an internal chamber, where a mechanism in the housing is utilized to periodically change the volume within the internal chamber so that a series of fluid vortices are generated and projected into an external environment out of the orifice. The mechanism may include a piston or diaphragm that is actuated by an electrical bias or piezoelectric element. The mechanism uses the working fluid where the actuator is being deployed such that linear momentum is transferred to the flow system without net mass injection into the system. In addition, a control system is utilized to oscillate the diaphragm so that a synthetic jet stream is propagated from the orifice.
Oscillatory fluidic actuators have proven quite effective for a variety of flow problems. However, several shortcomings associated with unsteady excitation must be solved before this technology is implemented into new flight worthy air vehicles. For example, oscillatory actuators are still in developmental stages, and their practicality and robustness require investigation for a realistic operational environment. In addition, pulsed excitation results in unsteady forces and moments with significant amplitudes, which is detrimental to structural integrity and has serious implications to structural fatigue. This is a particularly acute problem for a multi-element wing system where the slat and flap elements are deployed using systems of extendible linkages and tracks. The quality of boundary layer control due to unsteady force and moment excitation is also limited with oscillatory actuators. Furthermore, physical limitation of electrically driven actuators (diaphragm displacement, size of the orifice, and the size of the chamber) pose a limit on the maximum jet velocity and, thus, energy output. Combustion actuators produce higher jet velocity, but their energy output is also limited because of their small orifice. Although no air sources are required for combustion-powered actuators, these devices use combustible material that requires storage, supply lines, and firewalls within the airframe. Moreover, the potential hazard of combustion-based systems poses a major obstacle to market acceptance by aircraft operators and the general public.
It would therefore be advantageous to provide a system for controlling boundary layer flow over an aircraft wing. In addition, it would be advantageous to provide a system that improves aerodynamic performance of an aircraft wing. Moreover, it would be advantageous to provide a system that is easily employed with an aircraft wing for improving performance of an aircraft during take-off and landing.